As a kitchen equipment repair company we often have refrigerators with a deep malodorous aroma. However, we have many remedies both specific and and general to confront these affronts to the nose. Before talking about stench we have to establish its origins. Specifically, is the smell coming from big box, the coils inside or the coils outside.
Best case scenario and always your first course of action should be to empty out the big box and thoroughly clean it. For cleaning the inside of a commercial refrigerator I recommend starting by cleaning any debris, goop, Lettuce (there are always pieces of lettuce) etc that is visible. Then use a 5% bleach solution to wet the interior of the box. Clean the 5% bleach solution out of the box with dish soap and water. If you leave bleach in the box it will give the metal spots.
If once you have done this to abate the interior smell the smell persists we will look to the internal coil. It is possible mold has grown on the moist coil forming your smell. Take the following steps to remove the smell. Unplug the unit. If it is convenient set the unit out in the sun with the doors open. If not remove the cover usually on the top of the interior of the fridge. Clean what you can with soap and water keeping away from any electronics. The refrigeration coil’s performance is sensitive to bending so be gentle. Ideally at this point you would use a UV sterilizing light to kill the last of the mold. You can purchase these on Amazon for $20.00. If this is not possible a 5% bleach solution spray followed by water rinse spray should do the job. Of course proper coil cleaner is preferred.
For external smell we can skip straight to professional coil cleaning. Use compressed air followed by coil cleaner to remove the smell. However, if your coils are not visibly dirty it may be your condensate pan. Under the fridge will be a drip pan for catching the condensate from the refrigeration unit. Sometimes these take on a smell of their own. Remove it and clean it as you would a dish followed by a 5% bleach solution which you can leave on. If the pan has evaporated leaflets you may hand wash them and treat them with 5% bleach.
Of course if you are not comfortable with any of this or want a professional to clean all of the coils in your kitchen to keep your units operating as long as possible RJH can help.